A semiconductor light emitting element using nitride semiconductors such as gallium nitride is capable of emitting an ultraviolet light, a blue light, a green light and the like and has a high light emitting efficiency and property of low power consumption, as well as the semiconductor light emitting element is easy to reduce a size, resistant to, for example, mechanical vibrations and has a long life and high reliability. Therefore, applications of the semiconductor light emitting element to a large scale display, a traffic light, a backlight of a liquid crystal display and the like have rapidly progressed, recently.
The semiconductor light emitting element generally has a stack structure provided with a light emitting layer between a n-type semiconductor layer and a p-type semiconductor layer and emits a light by recombination of an electron and a hole injected into the light emitting layer from the n-type semiconductor layer and the p-type semiconductor layer, respectively. Therefore, a technology of how to efficiently extract the light generated in the light emitting layer is the important technology that determines a characteristic (efficiency) of the light emitting device.
Hence, a semiconductor light emitting element having a structure provided with an n-type semiconductor layer, an n-side pad electrode disposed on a part of the n-type semiconductor layer, a light emitting layer widely disposed on the n-type semiconductor layer so as to separate from the n-side pad electrode, a p-type semiconductor layer disposed on the light emitting layer, an insulator layer disposed on a part of the p-type semiconductor layer, a transparent electro de layer covering an exposed surface of the p-type semiconductor layer and the insulator layer, and a p-side pad electrode disposed at a position facing the insulator layer across the transparent electrode layer has been known (see, for example, Patent Documents 1 to 5).
The n-side pad electrode and the p-side pad electrode are connected to an external circuit (power source), respectively by wire bonding or bump bonding in order to apply a voltage between the n-type semiconductor layer and the p-type semiconductor layer. In the semiconductor light emitting element described above, a light emission just below the p-side pad electrode can be suppressed, and a light toward the p-side pad electrode from the light emitting layer is reflected to a side of a light emitting surface (a contact surface between the transparent electrode layer and the p-type semiconductor layer) by the insulator layer to be output from the light emitting surface. As a result, a high light emitting power can be obtained.
In addition, as an another example, a structure has been proposed, in which an electrode layer having a high contact resistance or a semiconductor layer having a low electrical conductivity is disposed on the p-type semiconductor layer, and the p-side pad electrode is disposed on the electrode layer, while contacting with a transparent electrode layer (see, for example, Patent Documents 6 to 8). In the structure, a light emission just below the p-side pad electrode is suppressed, thereby resulting in high light emitting power.
However, in the semiconductor light emitting elements disclosed in the Patent Documents 1 to 5 and the Patent Documents 6 to 8, there is a common problem that a disconnection in the transparent electrode layer is likely to be caused. Explanation will be given of the problem in reference to FIG. 8A and FIG. 8B. FIG. 8A is a cross sectional view schematically showing a structure in the vicinity of the p-side pad electrode in a conventional semiconductor light emitting element. As shown in FIG. 8A, a semiconductor light emitting element 110A has a structure in which an insulator layer, or an electrode layer having a high contact resistance, or a semiconductor layer having a low electrical conductivity (hereinafter, referred to as an insulator layer and the like 112) is disposed on a surface of a p-type semiconductor layer 111, a transparent electrode layer 113A is disposed so as to cover these layers, and a p-side pad electrode 114A is disposed at a position facing the insulator layer and the like 112 across the transparent electrode layer 113A. Since the transparent electrode layer 113A is generally formed by sputtering, a film thickness of the transparent electrode layer 113A becomes thin at a step portion S (side face portion of the insulator layer and the like 112) of the transparent electrode layer 113A indicated by dotted lines in FIG. 8A. As a result, a breakdown or disconnection (so-called open failure) is likely to be caused at the step portion S due to current concentration.
In order to solve the foregoing problem, another semiconductor light emitting element with a structure schematically shown in FIG. 8B has been proposed (see, for example, Patent Documents 9 to 13). A semiconductor light emitting element 110B has the structure, in which the insulator layer and the like 112 is disposed on a surface of the p-type semiconductor layer 111, a transparent electrode layer 113B having a height substantially identical to that of the insulator layer and the like 112 is disposed on the p-type semiconductor layer 111, and a p-side pad electrode 114B is disposed so as to cover the insulator layer and the like 112 and a part of the transparent electrode layer 113B. By setting a contact area between the p-side pad electrode 114B and the transparent electrode layer 113B to be large, the contact area is prevented from generating a current concentration.    [Patent Document 1] JPn. Pat. Appln. KOKAI Publication No. H08-250768    [Patent Document 2] JPn. Pat. Appln. KOKAI Publication No. H09-36431    [Patent Document 3] JPn. Pat. Appln. KOKAI Publication No. H09-129921    [Patent Document 4] JPn. Pat. Appln. KOKAI Publication No. 2004-140416    [Patent Document 5] JPn. Pat. Appln. KOKAI Publication No. H09-129922    [Patent Document 6] JPn. Pat. Appln. KOKAI Publication No. H11-4020    [Patent Document 7] JPn. Pat. Appln. KOKAI Publication No. H11-87772    [Patent Document 8] JPn. Pat. Appln. KOKAI Publication No. 2003-174196    [Patent Document 9] JPn. Pat. Appln. KOKAI Publication No. H10-173224    [Patent Document 10] Pamphlet WO98/42030    [Patent Document 11] JPn. Pat. Appln. KOKAI Publication No. 2000-124502    [Patent Document 12] JPn. Pat. Appln. KOKAI Publication No. 2002-353506    [Patent Document 13] JPn. Pat. Appln. KOKAI Publication No. 2003-124517